In a medical environment, and in particular in an operating theater, the lighting conditions should be appropriate for enabling a user, e.g. a surgeon or a physician, to work properly. In addition, good lighting should comply with certain standards and should deliver light having a color rendering index (CRI or Ra) lying in the range 85 to 100, and a color temperature lying in the range 3000 Kelvin (K) to 6700 K. More precisely, the term “color temperature” of light is used herein to mean the equivalent color temperature evaluated in conventional manner on the basis of the (x,y) chromaticity coordinates of the spectrum of the light in a chromaticity diagram of the International Lighting Commission (CIE).
In addition, in a medical environment, good lighting should offer uniform illumination, and high optical efficiency, without creating colored shadows in the field of illumination. Good lighting should also enable the surgeon to vary the color temperature and/or size of the illumination spot so as to adapt it to suit the surgeon's needs.
In addition, in an operating theater, the lighting device generally has a base fastened to the ceiling and from which an articulated arm extends that carries a lighting dome in which a plurality of lighting modules are disposed. Thus, it is desirable to achieve maximum compactness for the lighting dome above the operative field in order to make it easy for the user to handle the lighting dome.
The Applicant's Document EP 2 799 764 discloses a lighting device for forming an illumination spot of variable diameter and of variable color temperature. That device also makes it possible, by means of a beam splitter, to mix the white light beams of two different color temperatures coming from two white light sources so as to generate resulting mixed light beams at an intermediate color temperature. The optical system of that lighting device comprises a plurality of optical elements for focusing and combining the mixed light beams and for forming an illumination spot at an intermediate color temperature on the field of illumination. Those optical elements are constituted by an elliptical reflector and by a lens, which reflector and lens may be mounted to move relative to the beam splitter. In addition, in that lighting device, in order to reduce the divergence of the white light beams coming from the light sources, lenses are installed between the light sources and the beam splitter. That lighting device suffers from the drawbacks firstly of including a multitude of massive optical elements to be incorporated into the lighting dome, thereby making the structure more complex and heavier, and secondly of including an elliptical reflector, which is an optical part that is of costly and complex technical design.